Is Iapetus artificial?

[Cymric]

Hoagland is the prototype of a big crackpot with too much imagination and too little scientific background. His ideas are bogus, his reasoning unscientific: he postulates artificial constructs, and then 'finds' evidence to 'prove' that idea, instead of the other way around. The blowups are only impressive when you hve been preconditioned to think 'this could be artificial constructs', completely ignoring the fact we're looking at the utmost limit of magnification.

Not convinced? Well, where he makes a big slip is with the claim that 'any rocky body larger than a few hundred miles always turns into a sphere by the relentless force of gravity'. We can calculate that size pretty accurately. I found a reasonable approximation in the book Gravity From The Ground Up by Bernard Schutz, and works on the basis of the idea that the heat obtained from gravitational collapse onto a body of mass M is converted completely to thermal energy, kT. It disregards heat of fusion and the like, but for a first order estimate, it will do. When I plug in Iapetus' overall density and composition, I find that it lacks sufficient mass to melt completely and thus turn into a sphere. (2.7 * 10^22 kg required, Iapetus coming in at 1.7 * 10^22 kg.) However, it is a borderline case which accounts quite beautifully for the fact that Iapetus has such a 'squashed' appearance. It is big enough to melt part of its interior, but not big enough to pull itself into a spherical shape.

Hoaglands generalising claim needs a lot of 'ifs and buts' to stick, and it certainly won't work to complete satisfaction for Iapetus. And that is characteristic for much of the entire story. Beautiful pictures, definitely. But lousy arguments.

[Cymric]

falemagn wrote:
Whatever you think of Hoagland doesn't explain those pictures.

So we can leave Hoagland completely out of the equation, and just focus on what we observe about Iapetus. Are we in agreement there? Mind, I am not a planetary geologist, just an ordinary chemical engineer. Can I just ask you what your background is?

Well, I can't say anything about your numbers 'cause I haven't seen the calculations behind them, but I can point you to how things are in reality: Saturn's got many other moons, and many of them have a mass inferior to the one of Iapetus, yet they are perfectly spherical. I think you need to recheck your numbers ;-) Also, consider that not just mass counts, but also the diameter.

I was arguing against Hoagland's ridiculous claim that any body larger than a few hundred miles should be perfectly spherical due to gravitational self-attraction. That is not true: it depends on a number of parameters. Even my quickly scribbled calculations are likely to be off, since they assume that all energy to melt the objects interior comes from gravitational collapse. There is also tidal effects due to the proximity of larger bodies (think Io), heat of fusion (which is linked to composition), kinetic energy due to impacts with other bodies, and radioactive decay (which accounts for Earths still-molten interior). And then to top it all we have angular momentum to balance the attractive forces of gravity, and heat loss to space to determine the cooling time. All these factors have to be taken into account before one can say whether an object is likely to be spherical or not. Hoagland did not do this, and that was what I was trying to demonstrate.

Moreover, Iapetus doesn't appear to be just non spherical, it appeaars to be geodesic, which can't be explained by just saying that gravity wasn't strong enough to melt it.

My response would be 'so what?'. First of all, nowhere on that site is that claim made. Iapetus is a squashed ellipsoid. (Hoagland seems to suggest that because Iapetus' day is 79 Earth days long, it has always been that long, because the moon is still so squashed. He needs that line of reasoning to discredit natural phenomena. Out go tidal locking with Saturn, fast cooling and whatever else you can throw at it. Tsktsk.) Second, any body with materials which cannot cope with high tensile stresses will turn into a geodesic shape under its own gravity---that's what a geodesic means. The Earth is not a perfect ellipsoid, it is a geodesic because of its molten interior: angular momentum and gravitational self-attraction balance out at that particular shape. Third, I really wonder how one could measure the geodesic shape of Iapetus given the relatively crude instruments on Cassini. On Earth, the deviation from the ellipsoid is measured in meters.

That is in itself not an explanation for Iapetus' unusual shape, since I lack information about the various processes and their relevance. We'd need a geologist for that. What I am saying is that you shouldn't be jumping to conclusions either. There are plenty of quite normal mechanisms we understand at work (I've listed a few), and all we need to do now is put them in a very fast and very big computer to see what we end up with.
 

Notice I'm not saying Iapetus is indeed artificial, I'm just saying that unless you can explain in detail how could Iapetus "naturally" have such singular characteristics, then the artificial hypothesis can't be discarded.

Which is of course a complete and utterly bogus hypothesis, because you can't scientifically falsify that one. How would you determine it is constructed? Okay, I would call the presence of lorries, bulldozers and workers' huts a pretty good indication of artificiality. But other than that we have no idea what non-human constructs look like (other than evolved ones, like trees or birds) so we chose to  anthropomorphisize the entire thing. And that is certainly  not scientific.

Suppose that we see nothing indicating lorries on the new flyby in 2007, provided even that Cassini passes by so close that such devices can be seen with its cameras. If you then still cling to the artificial hypothesis, claiming some unknown way of construction, you chose to remain ignorant and not look at it in further detail. I would much rather prefer to keep on looking, improving my knowledge of geology and large-scale rock formations.

And it is quite possible that we will not be able to explain the particular rock formation in complete detail until we land probes on Iapetus, or visit the moon in person. Scientific theories are only as good as their underlying data, and that quite often means: work in progress. It's galling for me to realise I will probably not live to see the discovery of feasible FTL drives, wormholes, time travel, or---less ambitious---commercial fusion plants or quantum computers, but we can't have it all, can we? :-)

[Cymric]

Iceskaters are a poor analogy as the circling is quasi-two dimensional and not fully three-dimensional, and there is another force involved: friction between ice and skates.

In addition, I am sure you have the FEM calculations at your disposal to indicate why the smush seam would not be so even. If you don't, I suggest you ask Sandia Labs to perform simulations akin to these and see what turns up. I am not condemning the end result of such studies in advance; what I am saying is that you are glossing over a lot of important details which are bound to have an influence given the non-linearity of the problem.